Raman spectroscopy is used in many areas including pharmaceuticals, geology, chemical engineering, semiconductors, and the life sciences. More recently, Raman fiber sensors have been developed for minimally invasive applications in clinical histopathology. This paper describes the modeling, fabrication, and testing of filters directly deposited onto the excitation and collection fiber tips of a Raman probe. The narrow spectral width of laser rejection filters on the collection fibers should allow for the detection of low wavenumber Raman scattering within the “fingerprint” region. Deep blocking of the laser radiation is enabled by coating both ends of the collection fibers.
Multi-channel microscopy and multi-channel flow cytometry generate high bit data streams. Multiple channels (both spectral and spatial) are important in diagnosing diseased tissue and identifying individual cells. Omega Optical has developed techniques for mapping multiple channels into the time domain for detection by a single high gain, high bandwidth detector. This approach is based on pulsed laser excitation and a serial array of optical fibers coated with spectral reflectors such that up to 15 wavelength bins are sequentially detected by a single-element detector within 2.5 μs. Our multichannel microscopy system uses firmware running on dedicated DSP and FPGA chips to synchronize the laser, scanning mirrors, and sampling clock. The signals are digitized by an NI board into 14 bits at 60MHz – allowing for 232 by 174 pixel fields in up to 15 channels with 10x over sampling. Our multi-channel imaging cytometry design adds channels for forward scattering and back scattering to the fluorescence spectral channels. All channels are detected within the 2.5 μs – which is compatible with fast cytometry. Going forward, we plan to digitize at 16 bits with an A-toD chip attached to a custom board. Processing these digital signals in custom firmware would allow an on-board graphics processing unit to display imaging flow cytometry data over configurable scanning line lengths. The scatter channels can be used to trigger data buffering when a cell is present in the beam. This approach enables a low cost mechanically robust imaging cytometer.
Compact optical systems can be fabricated by integrating coatings on fiber tips. Examples include fiber lasers, fiber interferometers, fiber Raman probes, fiber based spectrometers, and anti-reflected endoscopes. These interference filters are applied to exposed tips – either connectorized or cleaved. Coatings can also be immersed within glass by depositing on one tip and connecting to another uncoated tip. This paper addresses a fiber spectrometer for multispectral imaging - useful in several fields including biomedical scanning, flow cytometry, and remote sensing. Our spectrometer integrates serial arrays of reflecting fiber tips, delay lines between these elements, and a single element detector.
Ultra-narrow band pass filters are used to maximize LIDAR range and sensitivity. Alternate designs and measured fabrication results are presented for sub-nanometer band pass filters down to quarter nanometer bandwidths with 95% transmission. Thermal and angle sensitivity have been minimized. The filters are fabricated using dual source, plasma assisted magnetron sputtering. Single and multi-cavity designs are presented.
A new approach for generating high-speed multispectral confocal images has been developed. The central concept is that spectra can be acquired for each pixel in a confocal spatial scan by using a fast spectrometer based on optical fiber delay lines. This approach merges fast spectroscopy with standard spatial scanning to create datacubes in real time. The spectrometer is based on a serial array of reflecting spectral elements, delay lines between these elements, and a single element detector. The spatial, spectral, and temporal resolution of the instrument is described and illustrated by multispectral images of laser-induced autofluorescence in biological tissues.
A new approach for generating high-speed multispectral images has been previously reported by our team. The central concept is that spectra can be acquired for each pixel in a confocal spatial laser scan by using a fast spectrometer based on optical fiber delay lines. This method merges fast spectroscopy with standard spatial scanning to create image datacubes in real time. The datacubes can be analyzed to define regions of interest (ROIs) containing diseased tissue. Firmware and software have been developed for selectively scanning these ROIs with increased optical power. This enables real time image-guided laser treatment with a spatial resolution of a few microns.
A new approach for generating high-speed multispectral images has been developed. The central concept is that spectra
can be acquired for each pixel in a confocal spatial scan by using a fast spectrometer based on optical fiber delay lines.
This concept merges fast spectroscopy with standard spatial scanning to create datacubes in real time. The spectrometer
is based on a serial array of reflecting spectral elements, delay lines between these elements, and a single element
detector. The spatial, spectral, and temporal resolution of the instrument is described, and illustrated by multispectral
images of laser-induced autofluorescence in biological tissues.
We present a new and innovative short-wave infrared (SWIR) hyperspectral imaging focal plane array (FPA)
concept for bulk and trace standoff explosives detection. The proposed technology combines conventional
uncooled InGaAs based SWIR imaging with the wavelength selectivity of a monolithically integrated solid-state
Fabry-Perot interferometer. Each pixel of the array consists of a group of sub-pixels in which each sub-pixel is
tuned to absorb a separate wavelength. The relative responses from the sub-pixels (i.e. wavelengths) are
compared to the spectral characteristics of explosives in the SWIR to detect and locate them within an imaged
scene among various background materials.
The novel technology will be compact, and consume low power such that it can be used as a handheld device or
mounted for persistent surveillance of crowded areas and checkpoints. The technology does not use any
scanning nor tuning apparatuses such as MEMS devices, and is therefore fast, compact, lightweight and not
susceptible to vibration. The technology is therefore ideal for man portable applications and unmanned vehicle
platforms. An eyesafe (covert) illuminator may be used to provide illumination in situations when ambient light
conditions are not sufficient. We will present a detailed design of the novel focal plane array and a theoretical
standoff distance and false rates study.
Pharmaceutical initiatives use analytical tools to monitor powders flowing through granulating, blending, and tablet
formation steps. Two critical parameters that drive the quality and efficiency of drugs are the concentration of actives in
the tablet, and the dissolution properties of the tablet. In order to ensure that these are within the target design space, it is
important that component concentrations, particle size distributions, and cluster size are monitored throughout the
manufacturing process. Standard optical techniques detect scattered light from spots that encompass many components
in the blend. Efforts to extract composition and blend uniformity based on chemometric analyses are complex and often
intractable. A highly spatially resolved spectral imager could simplify the chemometrics if the effective spatial
resolution can separate most particles from neighboring particles. The effective spatial resolution is a function of the
incident spot size, multiple scattering events, and the collection optics. This paper assesses the degree of spectral mixing
due to particle-particle scattering as a function of incident spot size. Our real-time optical design is enabled by a high
spectral brightness supercontinuum source, a MEMs-based spectral scan mechanism, confocal spatial scanning optics,
and high gain * bandwidth detection.
Line scan cameras are used for rapidly monitoring a moving web or sheet of material. Lighting for line scan inspection
should illuminate a long narrow rectangle, which is imaged onto the linear array of pixels in a line scan camera. This
distributed light source should provide a uniform power density at the desired wavelengths. Tungsten halogen lamps and
LED arrays can meet many of these objectives, but not in a highly directional beam with minimal thermal issues. We
have developed a new distributed light source that is based on diffracting light from a highly blazed grating written in the
core of a single mode fiber. The grating is blazed such that out-coupling is 90 degrees to the fiber axis. The fiber is
bonded to a cylindrical optic that collimates the azimuthal power distribution. Connecting a single laser diode to the
fiber can generate 1 milliwatt per square centimeter over a 10 cm by 0.5 cm rectangular region. Longer gratings and/or
multiple segments can be connected to illuminate longer regions. The distributed power density, spatial uniformity,
degree of collimation, and spectral bandwidth of these illuminated rectangles are reported. This highly directional
distributed source will enhance the utility of line scan cameras in multiple applications.
Since the 1990 discovery that porous silicon emits bright photoluminescence in the red part of the spectrum, light-emitting devices (LEDs) made of light-emitting porous silicon (LEPSi) have been demonstrated, which could be used for optical displays, sensors or optical interconnects. In this paper, we discuss our work on the optical properties of LEPSi and progress towards commercial devices. LEPSi photoluminesces not only in the red- orange, but also throughout the entire visible spectrum, from the blue to the deep red, and in the infrared, well past 1.5 micrometers . The intense blue and infrared emissions are possible only after treatments such as high temperature oxidation or low temperature vacuum annealing. These new bands have quite different properties form the usual red-orange band and their possible origins are discussed. Different LED structures are then presented and compared and the prospects for commercial devices are examined.